Well, this certainly triggered more conversation than I was expecting. I was simply wondering if there was such a method call, and apparently there isn't. That's okay.
I thought about this and decided to go with Yawning's suggestion to just use ADD_ONION and then record the returned RSA private key. It's easy enough to add that same key back into Tor whenever I want. There are several main advantages with this route, including isolating my software's data from Tor's and requiring fewer modifications to torrc. It just seems cleaner in general.